A hole-only organic semiconductor diode device is one type of single-carrier devices and is used as a power semiconductor device for a switch or a rectifier of a smart digital power integrated circuit. The hole transport material of the present invention can also be applied to organic electroluminescent devices and field effect transistors.
The hole-only organic semiconductor diode device is a device that is manufactured by spin-coating or depositing one or more layers of organic materials between two electrodes made of metal, inorganic compounds or organic compounds. A classical single-layer hole-only organic semiconductor diode device includes an anode, a hole transport layer, and a cathode. A hole injection layer may be added between an anode and a hole transport layer of a multi-layer hole-only organic semiconductor diode device, and an electron barrier layer may be added between the hole transport layer and a cathode. The electron barrier layer, the hole transport layer and the hole injection layer are composed of an electron barrier material, a hole transport material and a hole injecting material, respectively. After a voltage connected to the hole-only organic semiconductor diode device reaches a turn-on voltage, holes generated by the anode are transported through the hole transport layer to the cathode, and conversely, electrons cannot be injected from the cathode. The hole transport material in the hole-only organic semiconductor diode device can be applied to other semiconductor devices such as an organic electroluminescent device. The organic electroluminescent device has a huge market, so the stable and efficient organic hole transport material plays an important role in the application and promotion of organic electroluminescent devices, and is also an urgent need for the application and promotion of organic electroluminescent large-area panel display.
An existing hole transport material tris(4-carbazol-9-ylphenyl) amine (TCTA) which is frequently used in the market can basically meet the market demand of organic electroluminescent panels, but its efficiency and stability still need to be further improved because of its low glass-transition temperature (151° C.). The TCTA material has the disadvantage of easy crystallization. Once the hole transport material crystallizes, a charge transfer mechanism among molecules is different from an amorphous film mechanism that operates normally, resulting in a change in the hole transport properties. When the hole transport material is used in the organic electroluminescent device, the electrical conductivity of the entire device will change after a period of time, causing electron and hole charge mobility to become unbalanced, resulting in decrease of performance of the device and local short-circuiting possibly occurring in the device, and thereby affecting the stability of the device, and even resulting in failure of the device (Reference document: Journal of Applied Physics 80, 2883 (1996); doi: 10.1063/1.363140). Therefore, the demand for research and development of a novel hole transport material with a high glass-transition temperature is very urgent.